Ensure identity resolver is set when a credentials provider is given only at...

Ensure identity resolver is set when a credentials provider is given only at operation level (#3156)

Fixes https://github.com/awslabs/aws-sdk-rust/issues/901

This PR is a rework of https://github.com/awslabs/smithy-rs/pull/3021
whose fix was inadvertently discarded during
https://github.com/awslabs/smithy-rs/pull/3077. The way we fix the issue
is slightly different. In this PR, we add an identity resolver to
runtime components within `set_credentials_provider`, instead of using
`ServiceConfig.OperationConfigOverride`.

Added a Kotlin integration test to `CredentialProviderConfigTest.kt`
based on the customer reported issue.

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